1. Field of Invention
The present invention relates to an oscillator and a control method for controlling the oscillator, and more particularly, to an oscillator and a control method for controlling the oscillator which is for use in electronic equipment, such as a power-saving mobile telephone.
2. Description of Related Art
Electronic equipment can use a low power source voltage, and include circuits that only require low drive voltage, which saves power. Thus, an oscillator used in the electronic equipment can be driven at a voltage lower than that in conventional equipment.
As the voltage used for driving the oscillator decreases, however, the oscillator becomes more subject to operation environments, such as noise environments, power source environments, temperature environments, vibration environments, as well as variations in components. The oscillator remains unable to begin oscillating with an oscillation amplitude that does not grow at the start of oscillation, or remains unstable in the oscillation state thereof, although the probability of such troubles is very low.
In such a case, electronic equipment that includes the oscillator may not operate normally.
Particularly in electronic equipment, such as a mobile telephone, which intermittently repeats receiving operations for power saving, the number of start-ups of the oscillator is high, and the probability of aborted oscillation becomes high. It is therefore preferable to incorporate a preventive step in the oscillator.
The object of the present invention is to provide an oscillator and a control method for controlling the oscillator which reliably oscillates, even when the oscillator is driven at a low voltage.
To resolve the above problem, the present invention is an oscillator that includes an oscillator circuit, a driver that prompts the oscillator circuit to start oscillating by repeatedly performing drive control and drive stop control to the oscillator circuit, and a controller that controls the driver to prompt the oscillator circuit to start oscillating when the oscillator circuit is not oscillating, and that maintains the oscillator circuit in a driven state when the oscillator circuit is oscillating.
In the arrangement of the present invention, when the driver prompts the oscillator circuit to start oscillating, the controller controls the driver to continuously prompt the oscillator circuit to start oscillating based on the determination that the oscillator circuit is not oscillating when the count of the pulses of a pulse signal output from the oscillator circuit counted by the controller fails to reach a predetermined value during the drive control of the oscillator circuit, and the controller maintains the oscillator circuit in a driven state based on the determination that the oscillator circuit is oscillating when the count reaches the predetermined value.
In the arrangement of the present invention, the controller controls the driver to continuously prompt the oscillator circuit to start oscillating when no pulse signal output from the oscillator circuit is detected, and controls the driver to maintain the oscillator circuit in a driven state for a predetermined duration of time each time the pulse signal is detected.
In the arrangement of the present invention, the driver includes a switching device arranged on one of power supply lines to the oscillator circuit, and a switch controller that controls the switching device for on/off control with a period longer than the period of the pulse signal of the oscillator.
In the arrangement of the present invention, a control method for controlling an oscillator having an oscillator circuit, includes the steps of prompting the oscillator circuit to start oscillating by repeatedly performing drive control and drive stop control to the oscillator circuit when the oscillator circuit is not oscillating, and maintaining the oscillator circuit in a driven state when the oscillator circuit is oscillating.
In the arrangement of the present invention, in the control method for controlling an oscillator, the step for prompting the oscillator circuit to start oscillating includes repeatedly performing drive control and drive stop control to the oscillator circuit based on the determination that the oscillator circuit is not oscillating when the count of pulses of a pulse signal output from the oscillator circuit fails to reach a predetermined value during the drive control of the oscillator circuit, and maintaining the oscillator circuit in a driven state based on the determination that the oscillator circuit is oscillating when the count has reached the predetermined value.
In the arrangement of the present invention, the control method for controlling an oscillator circuit, the step for prompting the oscillator circuit to start oscillating includes repeatedly performing drive control and drive stop control to the oscillator circuit when no pulse signal is detected, and maintaining the oscillator circuit in a driven state for a predetermined duration of time each time the pulse signal is detected.